It is well known practice to transmit signals in two directions, along a common electrical wire transmitting system, a typical example being a telephone system. Telephone wire transmission systems are well known for transmitting voice transmissions and also for transmitting electronically generated signals from a wide variety of equipment such as security systems, facsimile machines, and a wide variety of computer information for example, coded signals concerning credit transactions, and transferring information to and from computers connected to the telephone wire system. Due to the nature of the telephone wire transmission systems, there are significant restrictions on the speed, and volume, of information which can be transmitted within a given time span. In the past this has not been a significant problem. However, with the ever increasing popularity of the so called "Internet", the ability to transmit very large volumes of information at high speed in both directions has become critical. The telephone wire transmission system does not readily accommodate itself to the very substantial expansion of the volume of information as well as the increase in speed of transmission that is required to satisfy the growing number of customers requiring Internet services. As a result, Internet servicing companies are seeking alternative means of transmission.
Telephone wire transmission systems are also subject to intermittent interference from a variety of sources, and are sometimes simply so overloaded that they are incapable of accepting further transmissions.
Coaxial cable transmission networks for distributing cable television services are becoming widely accepted in many cities and towns, and provide excellent services for distributing television signals to television sets of subscribers on the network. Such cable television distribution systems are based on a coaxial wire cable, having a single central conductive core, and a woven sheath of wire or other form of conductive sheath, insulated from the core. Such coaxial cable is capable of transmitting much greater volumes of information at high speed, and with very little interference. In the past such cable systems have been used for one way transmission of television signals from the head end signal source to the consumers television sets.
The existence of wide spread cable television signal networks has lead to the development of their use as a means of connecting consumers to the Internet system. The coaxial cable systems, with feed signal amplifiers located along the cables at spaced intervals, and with their substantial freedom from interference, lend themselves particularly well to the rapid transmission of high volume signals such as are generated by the Internet system. Consequently consumers are increasingly looking to the coaxial cable television networks as a means of connecting their computers to the Internet, so as to avoid the difficulties of connections via the telephone wire systems.
However, one of the problems encountered in using coaxial cable networks for distribution of Internet signals is that the cables are required to carry signals in both directions simultaneously. Thus the consumer will wish to be receiving signals from an Internet source, and will wish to be generating return signals, generated from his or her computer, back onto to the Internet. In theory the coaxial cable networks are ideally suited to this type of two-way transmission. In practice however, there are problems which arise from the original design of such cable systems. Since the coaxial cable networks are relatively long, the feed signals on the networks gradually become attenuated and decrease in strength as they pass along the length of the cable. In the case of television feed signals this problem is overcome, as mentioned above, by the use of feed signal amplifiers located in the coaxial cables at spaced intervals. These feed signal amplifiers ensure that all subscribers on any particular cable network will receive television signals (and Internet signals) of adequate strength, and they will also amplify the Internet feed signals, so that in spite of the considerable length of any one particular cable, the feed signals will all be substantially of the same signal strength to all households on that cable network.
However, such feed signal amplifiers are capable only of amplifying the feed signals fed into the coaxial cable from the head end where the television and Internet signals originate, and cannot amplify return signals, passing in the opposite direction.
As a result, when it is attempted to adapt or modify the coaxial cable system for two-way transmission, the return signals are unable to pass through the feed amplifiers already incorporated in the network. Return signal amplifiers have been used to amplify the return signals, and these return signal amplifiers are located alongside the feed amplifiers on the cable network and pass the return signals around the feed amplifiers, and increase the return signal strength. In this way the return signals bypass the feed signal amplifiers, and at the same time their signal strength is maintained at the desired level so that it can be fed back to the Internet server.
The problem of signal strength is aggravated by the fact that the attenuation of signal strength is greater in the higher range of frequencies, and is lower in the lower range of frequencies. The feed amplifiers in use on cable systems are already designed to overcome these problems, and equalise the signal strength over the entire frequency band of the feed signals. However, the adaptation of an existing one way cable network to accept return signals such as Internet signals requires that the return amplifiers be installed on the already existing cable network.
The return amplifiers designed for maintaining signal strength of the return signals must be designed so as to amplify the signals over the entire frequency range of the return signals back up to a uniform level of signal strength, across the entire range of frequency. However the signal strength of the return signals at any given location on an existing cable network can only be determined by actually measuring the return signals at that location. This signal strength will vary from one location to another. Consequently the return amplifier cannot be produced as a standard item, but must have performance characteristics which vary from one cable location to another.
Typically, the return frequency signals will be in the range of from about 5 to 42 megahertz. If the amplification of the signals does not produce a uniform signal strength over this entire range then the signals received back at the origin of the feed signals, i.e. the Internet server, will be distorted.
Another problem in the design and construction of such return signal amplifiers is the fact that return amplifiers will be required at spaced locations along any given length of coaxial cable in the system. These locations will correspond to the locations of the already installed feed signal amplifiers. Return amplifiers with standard characteristics will not be equally suitable at each location. In fact, it will be found that before a return amplifier is installed by the installer, the return signal strength at that location must be tested and a return amplifier must be installed having the correct amplifying characteristics for that particular location in the coaxial cable network. These specifications will vary from one return amplifier location to another along any given length of the coaxial cable.
In theory it is perfectly possible to manufacture a whole range of return amplifiers having a range of different performance characteristics. A coaxial line crew could carry a large supply of such return amplifiers with them, and after testing and checking the signal strength at a particular location, could then select and insert the appropriate return amplifier having the correct specifications for that location. In practice however this is not possible, since it will require a very large investment for supplying an adequate inventory of return amplifiers covering a full range of characteristics, to each particular line crew. In addition, transporting such a large inventory of return amplifiers covering a wide range of different characteristics, presents a problem of transporting a large number of bulky and relatively heavy objects.
A further problem is the fact that the line crew will be required to climb up to the coaxial cable and then check the signal strength and then come down and select the appropriate return amplifier and then climb back up again and insert it.
For all of these reasons, providing an adequate number of return amplifiers having ranges of different characteristics to meet all conditions and requirements on a given coaxial cable network becomes a logistical nightmare, and a severe financial strain, and causes much undesirable additional labour.
For all of these reasons therefore it is desirable to provide a uniform standardized return amplifier circuit, contained in a standardized return amplifier housing, and having a plurality of plug-in components, which can simply be carried in the personal equipment of the lines person. After climbing up to the cable the lines person can simply attach and connect the standardized return amplifier, and then test the signal strength and characteristics and then insert the appropriate plug-in components to produce a return amplifier having the necessary characteristics for that particular location in the system.
This problem is further complicated by the fact that return amplifiers have two separate circuit components that must be preset for any particular location. It is desirable that both of these circuits can be arranged to receive plug in sub components , which have the effect of presetting the characteristics of that amplifier . It is still further desirable that these plug in components shall be interchangeable as between the two circuits. In this way a lines person will be required to carry only one type of plug in component, in an adequate range of performance characteristics, so that when the signal strength has been measured at that location, the return amplifier can readily be set to the correct performance, by simply selecting the plug in components having the correct values for the two circuits.
This greatly reduces the requirement for carrying a large inventory of different return amplifiers and greatly reduces the financial burden of carrying such an inventory and also reduces the logistical problems and the time consuming effort by the lines crew of checking signal strength and then attaching the correct return amplifier.